1. Field of the Invention
The present invention relates to a data access apparatus and method for efficiently retrieving database resources distributed to a LAN (local area network) and a WAN (wide area network).
2. Description of the Prior Art
Recently, information retrieval systems with which a LAN is established within a company and connected to LANs established in other organizations such as companies, universities, research institutes, etc. through communications lines have been widely utilized to collect various information from a group of computer networks such as Internet, Intranet, Extranet, etc. A database accessed by such information retrieval systems is distributed through a network. For example, the database of a LAN of only one company (local database) is not sufficient in many cases. At this time, it is necessary to obtain information by accessing other databases (remote databases) through a communications line.
A conventional method for accessing such remote databases is the data access method and apparatus for accessing distributed databases as disclosed by Tokukai-hei 09-244939. This method associates each database with a remote database to set an access path, thereby reducing the concentration of the load onto a specific computer system in the inquiry process.
Another conventional system is the distributed system data referencing system as disclosed by Tokukai-hei 01-166247. According to this system, a retrieving process is performed on target data by searching the database site on which data is stored in order from the highest to the lowest in data access frequency when a remote database is searched.
There are the following problems with the above described conventional methods and apparatuses.
First, in the distributed database data accessing method and apparatus in Tokukai-hei 09-244939, the databases are searched in parallel. For example, since associated remote databases are accessed even if necessary data can be obtained from a local database, thereby charging the network and remote database with insignificant loads.
On the other hand, in the distributed system data referencing system according to Tokukai-hei 01-166247, a more frequently accessed database is retrieved by priority. It is not designed to retrieve a remote database through a network only when it is necessary to search remote databases. Therefore, since unnecessary database can be searched in the above described conventional system, thereby charging a network and a remote database with a large load.
The present invention aims at providing a method and an apparatus for reducing a load on a network and efficiently searching a database by decreasing access to unnecessary databases when a searching process is performed on a database having a high search evaluation.
That is, the above described aims according to the present invention can be attained by providing a data access apparatus for retrieving response data satisfying predetermined conditions based on a specific database in a distributed retrieval system in which a plurality of databases are distributed through a network. The data access apparatus includes: a retrieval unit for obtaining data satisfying the predetermined conditions as a response by retrieving the specific database; a count unit for counting the number of pieces of response data obtained by the retrieval unit searching the specific database; a retrieval request unit for requesting a search in another database in the network when the number of pieces of response data counted by the count unit does not reach a predetermined value; and a reception unit for receiving response data by searching the other database in response to the retrieval request from the retrieval request unit.
The specific database can be a local database directly connected to the computer to which a retrieval request is input, or a local database connected through, for example, an in-house LAN, etc. These databases can be accessed in a short time, and have a large volume of accumulated information related to the retrieval request. In addition, other databases in the network can be remote databases connected to other companies, research institutes, universities, etc. through Internet, public carriers, private lines, etc., require a longer access time, have a smaller volume of accumulated information, need a higher retrieval cost than the local database, and have lower evaluation orders.
As described above, the first aspect of the present invention has the configuration in which a retrieving process is performed on a specified database (local database) only, and issues a retrieval request to other databases (remote databases) through the retrieval request unit to supplement the insufficient number of pieces of response data when the number of response data does not reach a predetermined value.
Thus, the present invention has the configuration capable of reducing the load on a network and a remote database because no requests to search other databases are issued if the information obtained from the local database is enough.
Furthermore, the above described aims can be attained according to the second aspect of the present invention by providing a data access apparatus for retrieving response data satisfying predetermined conditions based on a specific database in a distributed retrieval system in which a plurality of databases are distributed through a network. The data access apparatus includes: a retrieval unit for obtaining data satisfying the predetermined conditions as a response by retrieving the specific database; a count unit for counting the number of pieces of response data obtained by the retrieval unit searching the specific database; a prediction unit for predicting the number of pieces of response data finally obtained as a result of searching the specific database according to the count information from the count unit and the information related to the specific database; and a retrieval request unit for requesting a search in another database in the network when the number of pieces of response data predicted by the prediction unit does not reach a predetermined value.
The second aspect of the present invention has the configuration in which insufficient response data can be supplemented from other databases by issuing a request to search other databases during the search in the local database if the predicted number of response data does not reach a predetermined value.
Thus, according to the second aspect of the present invention, the data retrieval time can be shortened by predicting the number of pieces of final response data obtained from a local database while reading data from the local database, and obtaining supplementary response data from a remote database when it is determined according to the prediction result that the necessary number of pieces of response data cannot be obtained.
In addition, the above described aims can be attained according to the second aspect of the present invention by providing a data access apparatus for retrieving response data satisfying predetermined conditions based on a specific database in a distributed retrieval system in which a plurality of databases are distributed through a network. The data access apparatus includes: a retrieval unit for obtaining data satisfying the predetermined conditions as a response by retrieving the specific database; a retrieval request unit for requesting an appropriate number of pieces of retrieved response data from another database when a request is issued to search the other database in the network: and a reception unit for receiving response data obtained as a result of searching the other database in response to the retrieval request from the retrieval request unit.
The retrieval request unit requests an appropriate number of pieces of retrieved response data from each database. The number of pieces of retrieved response data depends on, for example, the amount of accumulated data of each database, the retrieval speed for each database, a retrieval cost, etc.
With the above described configuration, data can be retrieved corresponding to the structure and the function of each database, thereby efficiently retrieving data.
Furthermore, when a predetermined number of pieces of response data is obtained during the data retrieval, a retrieval stop request is issued through a network to other databases (remote databases) being searched. By stopping searching other databases, an unnecessary retrieving process can be omitted, and a load on a network and other databases can be reduced.
In addition, according to a further aspect of the present invention, all databases including a specific database can be designed in a hierarchical structure, and a database closer to the specific database in the hierarchical structure is searched by priority so that the databases can be searched in order from the highest retrieval evaluation. Thus, a data access apparatus and method can be provided with high retrieval efficiency without issuing unnecessary inquiries.